Thermoplastic resin molded articles for automobile parts and various electric appliance housings are sometimes subjected to metallizing treatment such as formation of a metal layer of copper, chromium, nickel and the like on the surface of a molded article by plating surface treatment, and formation of a metal layer of aluminum, chromium and the like on the surface of a molded article by a vacuum vapor depositing method, sputtering method and the like, for enhancing design and other functions.
Conventionally, in performing surface metallizing treatment by a vacuum vapor depositing method, sputtering method and the like on such a resin molded article, it is necessary to form an undercoat-treated layer by painting and plasma polymerization treatment, then, to form a metal layer (thickness: decades to several hundred nm) by a vacuum vapor depositing method and the like, for deleting irregularity on the surface of a molded article to obtain smoothness. Usually, thereafter, a top coat layer made of a silicon-based material and the like is formed for the purpose of protecting the metal layer. Thus, the metallizing treatment of a thermoplastic resin molded article requires complicated many processes and special apparatuses and expensive treating agents. However, there is conducted, recently, a so-called “direct vapor depositing method” in which a pre-treatment process of forming an undercoat-treated layer is abbreviated.
However, the design of a bright molded article obtained by this “direct vapor depositing method” varies significantly depending on the kind of a resin material and the surface condition of a resin molded article. In the direct vapor depositing method, particularly, obtaining beautiful bright appearance without surface hazing is one of important subjects.
For such a field, for example, Japanese Patent Application Laid-Open (JP-A) No. 2001-2869 discloses a thermoplastic resin composition excellent in direct vapor depositing property comprising a rubber-containing graft copolymer obtained by graft-polymerizing a vinyl-based monomer (styrene, acrylonitrile) to a rubber-like polymer having specific particle size distribution (polyorganosiloxane-based polymers, acrylate polymers and the like), and a hard copolymer obtained by copolymerizing an aromatic vinyl-based monomer, a vinyl cyanide-based monomer and optionally other copolymerizable unsaturated monomers.
Also, JP-A No. 2002-133916 discloses, as a lamp housing material for automobile lamp equipments, a rubber-reinforced styrene-based resin composed of a graft polymer obtained by polymerizing an aromatic vinyl-based monomer (styrene, α-methylstyrene and the like) and a vinyl cyanide monomer (acrylonitrile and the like) in the presence of a rubber-like polymer having specific particle size distribution (polybutadiene-based rubber, ethylene-propylene-based rubber, acrylic rubber, silicone-based rubber and the like), or composed of a copolymer obtained by polymerizing the above-mentioned graft polymer and the above-mentioned monomer.
Automobile tail lamps, stop lamps, head lamps and the like are generally constituted of a lens made of a transparent resin such as PMMA (polymethyl methacrylate) resins, PC (polycarbonate) resins and the like, and a housing supporting the lens. Since such an automobile lamp housing is often exposed to sunlight outdoors, materials excellent in weather resistance are desired, in recent years.
Further, a so-called hot plate welding method is becoming general, in which in connecting a lens made of a transparent resin and a housing, a heated hot plate is pushed for several seconds to an adhesion part at which both materials are connected to heat-melt the both materials, and the hot plate is quickly removed, connecting the both materials. In the hot plate welding method, a phenomenon sometimes occurs in which each part of the both materials adheres to a hot plate of high temperature and stringiness occurs in removing the hot plate, therefore, it is important that this stringiness is scarce in using these materials.
As a material in such a field, for example, JP-A No. 10-310676 discloses, a hot plate welding thermoplastic resin composition composed of 10 to 100 parts by weight of a graft polymer obtained by graft-polymerizing at least one monomer unit selected from the group consisting of a vinyl cyanide monomer, an aromatic monomer, a (meth)acrylate monomer and other vinyl monomers in the presence of at least one rubber-like polymer selected from the group consisting of cross-linked acrylic rubbers and polyorganosiloxane-based rubbers, and 0 to 90 parts by weight of a copolymer composed of an aromatic vinyl-based monomer unit, a vinyl cyanide monomer unit and other vinyl-based monomer units.
JP-A No. 2000-336235 discloses, as a resin composition significantly improving stringiness in a hot plate welding method, an automobile lamp equipment lamp body resin prepared by compounding 3 to 30% by weight of a homopolymer of a methacrylate or a copolymer of monomer components containing a methacrylate as a main component in 97 to 70% by weight of a rubber-reinforced styrene-based resin.
Further, JP-A No. 2000-302824 discloses a thermoplastic resin composition containing a graft copolymer (A) having a rubber-like graft copolymer obtained by polymerizing 10 to 1000 parts by weight of (II) a monomer mixture composed of 50 to 100% by weight of a monomer unit composed of methyl methacrylate and/or styrene and 0 to 50% by weight of a monomer unit copolymerizable with the above-mentioned monomer unit, to 100 parts by weight of (I) a rubber-like copolymer obtained by polymerizing a monomer mixture containing an alkyl acrylate monomer unit and a 1,3-butadiene monomer unit, as a thermoplastic resin composition performing excellent welding with a PMMA resin, PC resin and the like by vibration welding, showing excellent appearance of melted portions occurring in vibration welding and manifesting a good vibration welding property, and a molded body made of this thermoplastic resin composition.
However, the resin compositions excellent in a direct vapor deposition property disclosed in JP-A Nos. 2001-2869 and 2002-133916 are not necessarily sufficient for responding a recent high requirement level for brightness. Furthermore, in applications such as an automobile lamp housing and the like, it is necessary that a molded article additionally has high weather resistance level. By further reducing the amount of the rubber component having large particle size specifically suggested in JP-A No. 2001-2869, brightness of higher level can be manifested, however, in this case, decrease in impact resistance and weather resistance is often remarkable, and it is difficult to simultaneously satisfy brightness by direct vapor deposition treatment, impact resistance and weather resistance. Also, a hot plate welding property is often not satisfactory.
On the other hand, in the case of formation of a layer made of metal such as aluminum, chromium and the like by a direct vapor deposition method, on the resin compositions disclosed in examples of JP-A Nos. 10-310676 and 2000-336235, sufficient brightness is not necessarily obtained and, level recently required is not attained in some cases.
Regarding the thermoplastic resin composition described in examples of JP-A No. 2000-302824, disclosed is gloss retention after an exposure time of 500 hours in an accelerated exposure weather resistance test by a sunshine weather meter, however, sufficient weather resistance is not obtained for exposure of further longer time and level recently required is not necessarily attained.